This invention relates to a method of correcting laser beam intensity, a laser beam intensity correction mechanism and a laser oscillation device having the laser beam intensity correction mechanism and, more particularly, to a method of correcting laser beam intensity, a laser beam intensity correction mechanism and a laser oscillation device which are suitable for being used in a laser beam welding machine irradiating a plurality of laser beams at a time.
A laser beam welding machine is generally used for joining metals together. In this laser beam welding, a laser beam emitted from a laser generator or oscillator is converged on a joint portion of a welding member on a stage by an optical system such as an optical fiber and a lens, and then a fused junction is applied thereto. For example, when plate-shaped welding members 14b shown in FIG. 11 are jointed together by laser welding, a laser beam 16 is irradiated onto one end of a joint surface by an emitting unit 13, and continuous welding is performed by moving the stage or by moving an irradiation point of the laser beam 16.
On the other hand, with a progress of technical fields such as an optical communication and an optical information processing, engineering development for connecting each of optical fibers with optical fiber connectors has been progressed. When members such as the optical fiber connectors which require an accuracy in positioning are welded by the laser welding, pulse welding which irradiates pulsed laser beams to several points of the joint surfaces at a time and conducts an instant fused junction is used as shown in FIG. 12.
In this method, since the laser beams are irradiated to several points of the joint surface, the laser beam emitted from the laser oscillator is splitted into a plurality of optical paths by beam splitters. A constitution of the laser oscillation device of the laser welding machine using such multi-branched laser beam is explained by reference to the accompanying drawings. FIG. 10 is a top plan view schematically illustrating a constitution of a conventional laser oscillation device.
As shown in FIG. 10, the conventional laser oscillation device includes; a laser oscillator 7 oscillating a laser beam; a total reflection mirror 8; beam splitters 9a and 9b leading the laser beams to optical paths 1 and 2, respectively; a total reflection mirror 9c leading the laser beam to an optical path 3; filters 17 adjusting the laser beam intensity in each optical path, optical systems 11 leading each of the laser beams to each of optical fibers, respectively; optical fibers 12; and connectors 5. FIG. 10 shows the constitution in which the laser beam is diverged into three optical paths.
Here, the laser beams, each having an equal power, need to be diverged into each of the optical paths 1 to 3, and thus the beam splitter 9a has a constitution in which one-third of the laser beam is reflected and other two-thirds thereof are transmitted. The beam splitter 9b has a constitution in which one-second of the laser beam having transmitted the beam splitter 9a is reflected and other one-second thereof is transmitted. In the optical path 3, there is provided a constitution in which the laser beam having transmitted the beam splitters 9a and 9b is totally reflected. Accordingly, the laser beam divided into three equal parts is made incident onto each optical path, however, in fact, reflectance and transmittance of the beam splitters 9a and 9b include a margin of error on fabrication and there arises dispersion of intensity of the laser beam being made incident onto each optical path.
The filters 17 are conventionally set between the beam splitter 9a, the beam splitter 9b or the total reflection mirror 9c and each of the optical systems 11, respectively. The filter with low transmittance is set to the optical path with high laser beam intensity so that the laser beam of each optical path is equal to others in intensity. The filter with high transmittance is, in reverse, provided to the optical path with low laser beam intensity so as to adjust the laser beam intensity.
As described above, the laser beam intensity is adjusted by inserting each of the filters 17 to each of the optical paths 1 to 3 corresponding to a division ratio of the laser beam in the conventional laser oscillation device. However, the transmittance of the each of the filters 17 to be inserted cannot suitably be adjusted. Thus, the filters 17 having transmittance which is closest to a desired transmittance are selected from a group of filters with a predetermined transmittance (for example, transmission filter of 99% and transmission filter of 95%). Since such filters are inserted to the optical paths so as to adjust the laser beam intensity, a fine adjustment cannot be conducted, although a rough adjustment is applicable. Also, laser beam intensity in each optical path cannot equally be divided with strictness and smoothness.
If the laser beam intensity in each optical path is slightly different, for example and when optical fiber connectors 14a are, as shown in FIG. 12, welded by a laser beam welding, each of welding spots with high laser beam intensity is highly fused as compared to other parts thereof, so that there arises dispersion of contraction when welding members is solidified with each other. As a result, a dislocation arises in each of the optical fiber connectors 14a, which make the optical fiber connectors useless as optical fiber connectors.
In the above method of correcting laser beam intensity, the laser beam intensity in each optical path is adjusted to be equal to others by using the filter with the conventional transmittance, so that the loss of the laser beam in each optical path is increased according to a combination of the filters 17. There causes a problem that a desired laser output cannot be obtained.
Further, when the margin of error is caused in a division ratio by a dislocation, characteristic changes with the elapse of the time or the like in the laser oscillator 7, the beam splitters 9a and 9b, the total reflection mirror 9c or the like, the error needs be corrected. However, in the above method of adjusting by detaching the filters, the filters 17 are taken out by disassembling the laser oscillator once, and are selected again and mounted after measuring the laser beam intensity in each optical path. There arises a problem that the above method requires much time for maintenance.
An object of the present invention is to provide a method of adjusting laser beam intensity readily and smoothly and to provide a laser beam intensity correction mechanism.
Another object of the present invention is to provide a multi-branched laser oscillation device having the correction mechanism.
In order to solve the above problems, according to the present invention, the method of correcting laser beam intensity comprises the steps of rotating an optical substrate around an optical axis of a laser beam as a rotation axis while maintaining an incident angle of the laser beam thereto, the optical substrate being located in a manner that the incident angle of the laser beam is set at a Brewster""s angle and of varying transmission intensity of the laser beam.
In addition, the method of correcting laser beam intensity for a laser oscillation device including a plurality of laser beam paths, a rotation cylinder freely rotating around an optical axis of the laser beam as a rotation axis and an optical substrate fixed at a predetermined slope angle with respect to the optical axis of the laser beam in the rotation cylinder, comprises the steps of: rotating the optical substrate around the optical axis as the rotation axis while maintaining the slope angle by rotating the rotation cylinder; and adjusting the laser beam intensity in each optical path to be equal to others.
A laser beam intensity correction mechanism of the present invention comprises an optical substrate rotating around an optical axis of a laser beam as a rotation axis while maintaining an incident angle, wherein the optical substrate is located in a manner that the incident angle of the laser beam is set at a Brewster""s angle, thereby varying transmission intensity of the laser beam by rotating the optical substrate.
Moreover, the laser beam intensity correction mechanism of the present invention comprises a rotation cylinder freely rotating around an optical axis of a laser beam as a rotation axis and an optical substrate fixed at a predetermined slope angle with respect to the optical axis of the laser beam in the rotation cylinder, wherein the optical substrate is rotated around the optical axis as the rotation axis while maintaining the slope angle by rotating the rotation cylinder and transmission intensity of the laser beam is varied. In the present invention, the slope angle of the optical substrate is set in a manner that the incident angle of the laser beam is set at the Brewster""s angle. In addition, it is preferable that the optical substrate is made of a quartz plate and a fine adjustment is realized by providing an antireflection coating on at least one surface of the optical substrate.
Further, according to the present invention, the laser oscillation device comprises a laser beam source, a first optical system for splitting the laser beam emitted from the laser beam source into a plurality of optical paths and a correcting arrangement for correcting laser beam intensity provided in at least one optical path, wherein the correcting arrangement includes a rotation cylinder being freely rotated around an optical axis of the laser beam as a rotation axis and an optical substrate slantly fixed in a manner that the incident angle of the laser beam is set at the Brewster""s angle, thereby adjusting transmission intensity of the laser beam in a manner that the laser beam intensity in each optical path is equal to others.